Use webp in path only when webp is supported
Add path format version to file result storages

Test Plan:
make test
Pillow test_requirement match setup.py
Don't use quality=keep when original image is not a JPEG or when quantization table is invalid
Fixes issues with GraphicsMagick and gif images. Fixes #163.
Correctly call engine's paste method (fixes #273)
Installing pexif from untrusted source
Merge pull request #278 from scorphus/master

Correctly call engine's paste method (fixes #273)
Merge pull request #263 from robolson/master

Pillow dep in test_requirement should match setup.py
Initial version of a convolution matrix filter, groundwork for future gaussian blur and edge detection filters.
Backup FILTERS_AVAILABLE prior to changing it (fixes #279)
Add new filter to expected list of filters
Revert "Installing pexif from untrusted source" (fixes #270)

This reverts commit adbb51c75bbb0d5c1268b84413e99b7f33dbe572.

pexif 0.13 now installs from PyPI, see bennoleslie/pexif#3
Merge pull request #282 from scorphus/pexif

Revert "Installing pexif from untrusted source" (fixes #270)
Merge pull request #281 from scorphus/convolution_test

Add new filter to expected list of filters
Merge pull request #280 from scorphus/master

Backup FILTERS_AVAILABLE prior to changing it (fixes #279)
Implement convert_to_grayscale in opencv engine (fix #274)
Merge pull request #283 from scorphus/master

Implement convert_to_grayscale in opencv engine (fix #274)
Basic gaussian blur filter, performance can be further improved in the future
Pass log level through upstart script